High performance distributed system of record with unspent transaction output (UTXO) database snapshot integrity

ABSTRACT

A method operative in association with a set of transaction handling computing elements that comprise a network core that receive and process transaction requests into an append-only immutable chain of data blocks, wherein a data block is a collection of transactions, and wherein presence of a transaction recorded within a data block is verifiable via a cryptographic hash, and wherein Unspent Transaction Output (UTXO) data structures supporting the immutable chain of data blocks are maintained in a UTXO database, wherein a UXTO is an output from a finalized transaction that contains a value. The technique herein includes periodically snapshotting a given portion of the UTXO database to generate a hash. The hash of the snapshot is recorded within the immutable chain of data blocks, and preferably within a given block header. In responsive to a receipt of a recovery request, and to facilitate recovery of the system to a provably-known state, a consensus algorithm is executed over the UXTO snapshot.

BACKGROUND Technical Field

This application relates generally to managing a distributed system ofrecord across a set of computing resources in a distributed network.

Brief Description of the Related Art

Distributed computer systems are well-known in the prior art. One suchdistributed computer system is a “content delivery network” (CDN) or“overlay network” that is operated and managed by a service provider.The service provider typically provides the content delivery service onbehalf of third parties (customers) who use the service provider'sshared infrastructure. A distributed system of this type typicallyrefers to a collection of autonomous computers linked by a network ornetworks, together with the software, systems, protocols and techniquesdesigned to facilitate various services, such as content delivery, webapplication acceleration, or other support of outsourced origin siteinfrastructure. A CDN service provider typically provides servicedelivery through digital properties (such as a website), which areprovisioned in a customer portal and then deployed to the network.

A blockchain is a continuously growing list of records, called blocks,which are linked and secured using cryptography. Each block typicallycontains a cryptographic hash linking it to a previous block, andtransaction data. For use as a distributed ledger, a blockchaintypically is managed by a peer-to-peer network collectively adhering toa protocol for validating new blocks. Once recorded, the data in anygiven block cannot be altered retroactively without the alteration ofall subsequent blocks, which requires collusion of the network majority.Blockchains are suitable for the recording of events, various recordsmanagement activities (such as identity management, transactionprocessing, documenting provenance, etc.) and others. Generalizing, ablockchain is a decentralized, distributed and digital ledger that isused to record transactions across many computers so that the recordcannot be altered retroactively without the alteration of all subsequentblocks and the collusion of the network. In a typical blockchain, blockshold batches of valid transactions that are hashed and encoded into adata structure. In this structure, and as noted above, each blockincludes the cryptographic hash linking it to the prior block in theblockchain. The linked blocks form a chain. This iterative processconfirms the integrity of the previous block, all the way back to theoriginal genesis (or first) block.

Blockchain implementations may be used to support a variety ofapplication areas, some of which have elevated security requirements. Inknown systems, such as Bitcoin, Etherium and their derivatives, a mainfocus is on securing the private keys that are used by wallets (namely,to spend value associated with the wallet). In addition, wallet securitycontinues to be an important consideration in the design andimplementation of such systems, and there are also a set of extended usecases, e.g., hosted or server-based wallets, server based co-signing ormultiple signature-based transactions, and administrative management ofaccounts and associated value, that present additional securitychallenges. In particular, these capabilities offer significantbenefits, but they may also increase the attack surface, i.e., thenumber of and paths of potential compromise.

BRIEF SUMMARY

This disclosure provides for a high performance distributed ledger andtransaction computing network fabric over which large numbers oftransactions (involving the transformation, conversion or transfer ofinformation or value) are processed concurrently in a scalable,reliable, secure and efficient manner. In one embodiment, the computingnetwork fabric or “core” is configured to support a distributedblockchain network that organizes data of the blockchain in a mannerthat allows communication, processing and storage of blocks of the chainto be performed concurrently, with little synchronization, at very highperformance and low latency, even when the transactions themselvesoriginate from remote sources. This data organization relies onsegmenting a transaction space within autonomous but cooperatingcomputing nodes that are configured as a processing mesh. Each computingnode typically is functionally-equivalent to all other nodes in thecore, and preferably each node can carry the entire load of the system.A computing node typically comprises a cluster of computing,communications and storage elements. More generally, all computing nodesthat comprise the core network preferably are considered to be equal toone another, and no individual node, standing alone, is deemed to betrustworthy. Further, with respect to one another, the nodes operateautonomously, and preferably no node can control another node. The nodesoperate on blocks independently from one another while still maintaininga consistent and logically complete view of the blockchain as a whole.

In one embodiment, the processing core is accessible via edge networks,e.g., the edge servers of an overlay network, such as a CDN. In thisembodiment, a CDN edge network supports a globally-based distributedsystem that provides a message processing service, wherein messages areassociated with transactions. End user machines and services interactinitially with the CDN edge network, which then routes transactionsrequests and responses to and from the core, with the core supporting adistributed system of record.

One preferred design of the above-described system involves segmentingblocks of transactions and partitioning so-called Unspent TransactionOutput (UTXO) data structures. To allow recovery of the high performancedistributed system of record without the necessity to start with thegenesis block, a system that creates a snapshot of the data periodicallyis required. Because the snapshots are necessarily large, and because ittakes considerable time to create them, typically it is not possible todetermine a hash of a snapshot at the blocktime that is represented bythe snapshot. At the same time, and in order to maintain the correctnessproperties of the blockchain, it is necessary to record a hash of thesnapshot, wherein the hash of the snapshot certifies the authenticity ofthe snapshot. The technique herein provides such support but withoutrequiring the hash to be stored externally, thereby facilitatingself-verifiability of a blockchain/UTXO database snapshot. Preferably,this is accomplished by recording on the blockchain a hash or otherdigest representation of the snapshot, and then enabling entities tocarry out a consensus agreement over the UTXO snapshot.

The foregoing has outlined some of the more pertinent features of thesubject matter. These features should be construed to be merelyillustrative. Many other beneficial results can be attained by applyingthe disclosed subject matter in a different manner or by modifying thesubject matter as will be described.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the subject matter and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram illustrating a networking architecture thatprovides a distributed system of record with transactions organized intoa blockchain according to this disclosure;

FIG. 2 depicts a block segmentation according to the technique herein;

FIG. 3 depicts a segmented blockchain;

FIG. 4 depicts a segment migration and reassignment process;

FIG. 5 depicts an inter-node segment handling process of thisdisclosure;

FIG. 6A depicts a representative computing node block diagram and itsoperation while performing transaction validation;

FIG. 6B depicts the computing node of FIG. 6A and its operation whileperforming block mining and verification;

FIG. 7 is a high level depiction of a concurrent processing technique ofthis disclosure;

FIG. 8 is a detailed depiction of the operations that are carried outamong various nodes and node elements to provide streaming blockgeneration, transmission and validation according to this disclosure;

FIG. 9 depicts a content delivery network (CDN) architecture that may beassociated with the computing network fabric;

FIG. 10 depicts a representative machine configuration; and

FIG. 11 depicts a UTXO snapshot technique of this disclosure.

DETAILED DESCRIPTION

Overall High Level Design

FIG. 1 depicts a scalable, high performance architecture forimplementing a distributed system of record with transactions organizedinto a blockchain. At a high level, the system is divided into multiplefunctional areas as shown, namely, a periphery 100 a, an edge 100 b, anda core 100 c. The system may comprise other functional areas tofacilitate delivery, administration, operations, management,configuration, analytics, and the like, but for simplicity these areasare not depicted. As used herein, the periphery 100 a refers generallyto elements associated with a boundary 101. These elements typicallyinclude client-server based electronic wallets or wallet devices,terminal and point of sale devices, legacy financial network elementsand associated adapters. Generally, and as used herein, any elementinvolved with creating and consuming transactions including, withoutlimitation, financial transactions, may be an element in the periphery101. The periphery may extend globally. The edge 100 b typically refersto the elements of an overlay network associated with boundary 102.Representative elements include, without limitation, the processing,communication and storage elements (edge servers, switches/routers,disks/SSDs) running on an overlay edge network (e.g., a CDN such asAkamai®). A CDN such as described advantageously provides low latencypoints of presence (relative to the end users/devices) that aggregateand, as will be described, route requested transactions and theirassociated results (to and from elements in the periphery) efficiently.Wallet services may be located within the edge. The edge elements alsoact individually, collectively, and in conjunction with other servicesas a security perimeter protecting the core 100 c from attacks and otheradversarial activity. While a CDN-specific implementation is preferred,a typical edge network in the system herein need not be limited to a CDNedge network. Any suitable network, new or extant, could be usedincluding, without limitation, cloud-based systems.

The core 100 c refers to elements associated with boundary 103. As willbe described, preferably the core 100 c is a high performance network ofnodes that together support the processing and storage of transactionblockchain(s) meeting specified performance requirements including, butnot limited to, throughput, response time, security and data integrity.A node (sometimes referred to as a “computing node”) in this contexttypically is a cluster of computing, communications, and storageelements. More generally, a cluster as used herein refers to one ormore, and possibly many, computing, communications, and storageelements. In one embodiment, the core 100 c comprises overlay networknodes, although this is not a requirement, as the core 100 c maycomprise a set of nodes distinct from the CDN and dedicated to the coreoperations (as will be described). Typically, computing nodes areinterconnected by network transits and have a high degree ofinterconnectivity to reduce or eliminate topological bottlenecks.

To facilitate high performance, preferably the core network isconstructed using a high quality, high capacity, and diverseinterconnect. The particular configuration of the core network typicallyis implementation-dependent, at least in part based on the nature of theconsensus protocol that is implemented in the blockchain. Depending onthe consensus protocol used, the size of the core network (and/or thedistribution of various computing nodes therein) may also be constrainedas necessary to ensure sufficiently low latency network communicationsacross the core.

In one non-limiting implementation, the CDN edge 100 b supports aglobally-based service having associated therewith a core network 100 c(e.g., that is located across a plurality of networked data centers in agiven geography).

Referring again to FIG. 1 , message 104 is an example of a device (e.g.,an end user device, an electronic wallet, etc.) sending a transactionrequest to an edge server (e.g., such as a CDN edge server). It shouldbe appreciated that a multitude of such messages (and that will be sentto and processed by the core network as described herein) are expectedto originate from server, devices, and wallets worldwide. The messagesmay be transmitted over persistent connection or ephemeral connections,as well as via new or extant networks where those networks may be partof legacy or network infrastructure purpose built to natively supportthe system capabilities described herein. Further, messages may be sentto one or more edge servers to reduce reliance on any single point ofingress to the system.

Message 105 is an example of an edge element routing transactions(possibly including the one contained in message 104) to an appropriateelement in a core node 110 (a set of which nodes 110 are depicted). Fora given transaction there may be multiple messages 105 that route thesame transaction or a hash (or other digest) of the same transaction tothe appropriate element in other core nodes. It is not required that allmessages 105 contain a full representation of a transaction. A digest ofa transaction may be transmitted (1) to make core elements aware of theexistence of a transaction, and (2) to provide a robust way to check theintegrity of messages containing full transactions. This enablescomplete, yet efficient, propagation of incoming transaction messages tothe appropriate elements in all core nodes. It also greatly reduces thenetwork loading associated with traditional gossip protocols and yetprovides protection, e.g., from compromised edge elements censoring orcorrupting transactions.

Message 106 is an example of a core node element routing transactions tothe appropriate element in another core node. There may be multiplemessages 106, such that a core node element participates in propagatingtransactions or transaction digests across the core nodes of the system.Core nodes receiving message 106 may, in turn, generate other messages106, further propagating the messages across the core nodes of thesystem.

Topology-Aware Data Propagation

While any data propagation protocol may be employed, one preferredapproach herein is to improve upon cost and latency of traditionalrandomized peer-to-peer gossip protocols by shaping the propagation tothe underlying network topology. In concert, messages 104, 105, and 106comprise paths of propagation starting with topologically most proximateelements and reaching topologically less- or least-proximate elements. Adevice that sends messages 104 to other edge elements typically followsdifferent paths of propagation across the network. This is illustratedby the messages 107, 108, and 109 propagating in a different direction.Further, the path of propagation starting from a given device, ingeneral, may change over time to achieve proper load balancing andsecurity.

Service Discovery and High Performance Mapping

Again referring to FIG. 1 , before any messages are sent, each elementoriginating a message typically must discover the address of thereceiving element. An address may be an Internet Protocol (IP) addressor some other name or number in an address space in some type of network(e.g., peer-to-peer network or overlay network). Discovering the addressof another element can be achieved in a variety of ways but generallyinvolves sending a set of element attributes to a discovery service andreceiving address information in return. In one embodiment that ispreferred, the attributes of the system elements to be discovered areencoded as domain names, thereby allowing the system to use a CDN's highperformance domain name lookup services to return the necessary addressinformation. Using an overlay network's mapping technology offersseveral advantages. It supports large domain name spaces to enable eventhe largest scale deployments. This enables an edge element, forexample, to route transactions not just to a core node, but even tospecific elements in the core node that handles the associated portionsof the transactions' identifier space. This same type of fine-grainedrouting can be done for communications between core node elements; inparticular, and using CDN DNS services, an element in one node handlinga set of segments, partitions, or other groupings of transactioninformation can send messages directly to elements in other core nodesthat handle the same segments, partitions, or other groupings oftransaction information. This is advantageous because although trafficmay traverse a common set of low level network routers/switches, thecore nodes need not inspect and route each transaction individually. Theuse of the CDN name services in this manner also supportsreconfiguration. In particular, when a node's configuration changes, forexample, because responsibility for some portion of the transactionspace is transitioned from one server to another, the changes arequickly and efficiently communicated via the name service's mappingsystem. Another advantage of using the CDN name services supports thenotion of suspension. Thus, in the event an edge element or core nodeelement becomes impaired or inoperative, the mapping system can maptraffic away from the problem. A further advantage of using the CDN nameservice is the ability of such systems to support load balancing oftraffic based on high resolution capacity consumption measurements. Thisapproach also supports route and region diversity, such that a device inthe periphery may receive addressing information for edge elements thatshare minimal underlying service and network components. CDN DNSservices also support latency optimization. For example, core nodeelements may receive addresses for other core node elements that meetsome proximity criteria.

An alternative embodiment utilizes location or direction-aware mapping.Thus, for example, a core node element may use domain names encoded withlocation or direction information (either geographic or topologicaldirection) such that responses provide addresses to node elements thatare in a desired location or direction or that comprise a directionalgraph. This capability may be intrinsic to the mapping system or anadjunct thereto. Topological mapping in this manner provides for a lowlatency, topology aware data propagation mechanism.

Generalizations

As used herein, a block generally refers to any aggregation orassociation of transaction data. There is no specific format required. Ablockchain is a continuously growing list of records, called blocks,that are linked and secured using cryptography. Each block in ablockchain typically contains a cryptographic hash linking to theprevious block, and transaction data. For use as a distributed ledger, ablockchain is typically managed by a peer-to-peer network collectivelyadhering to a protocol for inter-node communication and validating newblocks. Once recorded, the data in any given block cannot be alteredretroactively without the alteration of all subsequent blocks, whichrequires collusion of the network majority.

While the techniques herein may use a blockchain to record transactiondata, this is not a limitation, as the architecture and associatedtransport mechanism of this disclosure system is also applicable toother organizations of transaction data. Moreover, the notion of ablockchain, as in a chain or sequence of blocks, may be any organizationof blocks including, without limitation, a block tree, a block graph, orthe like.

Mining is the act of generating an ordered block of transactions with aheader that references a previous block in the blockchain. In public(permissionless) blockchain consensus systems, mining generally isstructured as a competition; if a generated block (and its ancestors)survive the mining competition and subsequent consensus process, it isconsidered finalized and part of the permanent record. In an idealsystem, mining responsibility from one round to the next (i.e., from oneblock to the next) is randomly-dispersed across participants. Formally,in an ideal system, mining decisions are not predictable, not capable ofbeing influenced, and are verifiable. In real world applications,however, the dispersion need not be perfectly random. For example, inproof-of-work systems, the dispersion is not actually random, asentities with more mining power have a higher probability of winning thecompetition.

Segmentation

Traditional blockchain implementations treat the blockchain as a simplesequence of blocks. Such approaches severely limit the achievableperformance of blockchain implementations, typically by creatingbottlenecks in processing, communicating and storing the blockchain inits aggregate form.

In contrast, the approach described here departs from known techniquesby organizing the data of a single chain in a manner that allows itscommunication, processing and storage to be performed concurrently, withlittle synchronization, at very high performance. Preferably, and aswill be seen, this data organization relies on segmenting thetransaction space within each node while maintaining a consistent andlogically complete view of the blockchain. This approach may also beapplied to each of multiple chains that comprise a set of federated orsharded blockchains, and to improve the performance of the blockchainoperation thereby reducing the work and increasing the performance ofoff-chain (so-called “Layer-2”) systems.

In this approach, the consensus algorithm that spans the network is usedto ensure the system produces correct finalized results. The particularconsensus algorithm(s) that may be used are not a limitation. Operationswithin each node, however, assume the elements of the node are correctand trustworthy. If a node fails or is corrupted by an adversary, thesystem relies on the rest of the network to maintain service integrityand availability as well as to support failure and intrusion detectionfunctions. As will be seen, this design architecture enables theinternals of a node to be organized as a loosely-coupled distributedsystem running on a high performance, low latency communications fabricsuch that system elements are aligned with the blockchain dataorganization. The resulting architecture provides a much higherperformance implementation as compared to known techniques.

Block Segmentation

Referring to FIG. 2 , a block 200 is segmented by transaction id(Tx_(i)) into some number of segments 202 a-n, where n=1000, and aheader 204. The segments 202 and header 204 represent a block of theblockchain although they may be (and often are) processed, transmittedand stored separately. The number of segments 202, shown in FIG. 2 as1000, may be more or fewer in number and may change over time ordynamically. Preferably, a sufficient number of segments is selected tocreate a space that is large enough to enable substantial future growthof the underlying resources without having to change the segmentation(the organization) of the data.

In this embodiment, block segmentation typically is an externallyvisible attribute shared by all nodes of the network. As will be seen,organizing the block data by segment significantly improves theperformance and efficiency of nodes exchanging block information. Inparticular, the approach herein enables the components of a noderesponsible for handling a given segment to communicate directly withthe components of other nodes responsible for handling the givensegment. Moreover, the mapping of segments to components may differacross nodes, thereby allowing for scaled-up (or scaled-down)deployments, e.g., by allowing nodes to employ a different number ofresources in handling the overall amount of transaction data.

In an alternative embodiment, the details of the segmentation may remainstrictly a node internal attribute. In such an embodiment, the mappingof segments to the components of a node may be arbitrary. Thisalternative allows greater independence in the configuration of nodes,but it generally requires more granular (e.g.,transaction-by-transaction) exchange of data between nodes involvingsome form of transaction layer routing inside the nodes.

As used herein, the term segmentation is used to mean any grouping,partitioning, sharding, etc. of transaction data, whether implicit orexplicit, such that the elements of one node may interact with elementsin another node to exchange data for more than one transaction at atime.

A header 204 includes several required elements, namely, a hash 210 ofthe previous block header, a Merkle root 208 of the block's contents,and a proof 206 indicating that a miner of the block in fact was alegitimate miner. Other information may be included.

Blockchain Segmentation

Referring to FIG. 3 , the segmented blocks form, temporally, a segmentedblockchain, with some blocks thereof pending (i.e., not yet finalized),while other blocks thereof are finalized (i.e., added to theblockchain). In this example, each machine 300 as depicted supports bothpending and finalized blocks, although this is not a requirement. Thisdistributed organization is not limited to a block “chain,” as theapproach may also be applicable in other scenarios, such as with respectto a block tree or block graph structure. The approach is advantageousbecause the blocks are still whole but the segments thereof areprocessed more efficiently than processing a block monolithically. Asdepicted in FIG. 3 , a varying number of segments may be assigned todifferent machine resources and commingled. This type of organization isparticularly applicable to virtualized and containerized environments,although neither are required to achieve the benefits.

Referring to FIG. 4 , the assignment of segments to system resources mayvary over time, for example, to support upgrades, maintenance andfailure recovery. In this case, one machine 402 failed or was taken offline, and the segments it was handling are then migrated to othermachines. This approach fits well with established concepts of migratingvirtual or containerized computing elements both for routine andemergent reasons.

Segmentation and Inter-Node Communication

Referring to FIG. 5 , by making segmentation a publicized attribute of anode, elements within a node may communicate directly with elements inother nodes to exchange information on the granularity of a segment. Themapping of segments to nodes need not be the same across all nodes.

As will be described, in a preferred embodiment the computing nodes ofthe system are each capable of performing (and often do perform)multiple distinct functions or modes (operating roles) such astransaction validation, as well as block mining and verification.Indeed, a given computing node often operates in multiple such modes atthe same time. In a typical operating scenario, particular nodes may beused for mining, although typically all computing nodes verify what ismined.

FIG. 5 illustrates how orchestration of block mining and blockverification preferably is accomplished in the presence of segmentation.In this example, it is assumed that there are a number of machines thatare used for generating/mining the block in the computing node 500 a,while other computing nodes 500 b, 500 c and 500 d comprise machinesthat verify the block (referred to herein as “verification”). Asdepicted, a block mining event is initiated by message 502 sent by amining node 500 a (generally by the element that handles the generationand validation block headers) to the other nodes of the network (in thisexample, nodes 500 b, 500 c and 500 d) informing them that it is aboutto begin mining or generating a block. Corresponding elements in nodes500 b, 500 c and 500 d receive this message and inform their node'sprocessing elements to expect mined block data from elements in themining node. At the same time, multiple sequences of messages like 503are sent for each generated segment by the elements in the mining nodehandling those segments to the elements handling each segment in remoteverification nodes (respectively).

Once a mined segment is finished, message 504 is sent from the elementresponsible for that segment to the element responsible for the blockheader. The message includes, among other things, the Merkle root of thegenerated segment. Once all messages 504 are sent and received, theelement responsible for the block header creates the top of the blockMerkle tree and saves the Merkle root in the header. It then transmitsmessages 505 to the elements in the other nodes responsible for handlingheader generation and verification. In performing validation, and uponreceiving messages 503 for a segment, the receiving node elementhandling the segment validates the received transactions, computes thesegment's Merkle tree, and upon completion sends message 506 to theelement in the node handling the header. That element reconstructs theblock header from the messages 506 for all segments and compares it tothe header received from the mining node in message 505. If the headersmatch, the block is accepted and added to the set of pre-finalizedblocks in that node.

In one embodiment, if the transactions fail to verify or thereconstructed header does not match the header transmitted from themining node, the block is rejected, and all changes are reverted andexpunged from the node.

In another embodiment, validating nodes can flag machines that mine to adifferent value of message 506 for the same segment, therebysafeguarding the system from one or more faulty or malicious machines.

The above-described processing is described in more detail below.

Segmentation and Node Orchestration

FIG. 6A and FIG. 6B depict the operation of a computing node of thesystem, with FIG. 6A showing the operation of the node elements involvedwith initial transaction validation, and FIG. 6B showing the operationof the node elements involved with block mining and verification.

As depicted in FIGS. 6A and 6B, a node comprises several elements orcomponents that work together to perform separately scalable tasksassociated with transaction validation as well as block mining andverification. These components include node coordinator 601, a set ofsegment handlers 604, a set of transaction handlers 609, a set of UTXO(Unspent Transaction Output) handlers 614, and a set of signatureverifiers 617. While segment and transaction handlers are shown asdistinct (and this is preferred), these functions can be combined into acomposite handler that performs both functions as will be described.Further, while typically there are a plurality of instances of eachhandler, one may suffice depending on its processing capability.

By way of background, and as noted above, preferably each node isfunctionally-equivalent to all other nodes in the system, and each nodecarries the entire load of the system. More generally, all nodes in thesystem are considered to be equal to one another and no individual node,standing alone, is deemed trustworthy. Further, with respect to oneanother, the nodes operate autonomously, and no node can control anothernode.

A node operates in general as follows. For transaction validation, andwith reference to FIG. 6A, raw transactions are continuously received atthe node at 612, typically as those transactions are forwarded from theedge machines (or from other nodes), and initially processed by thetransaction handlers 609. A transaction typically is formulated in awallet or a set of wallets (e.g., by a wallet service associatedtherewith or running thereon), and the wallet typically interacts withan edge machine either to receive a transaction request from theperiphery or to forward a blockchain transaction to the core, where itis received at 612 and processed by a transaction handler 609. Ingeneral, the processing of a raw transaction by a transaction handler isa “validation,” and once a raw transaction is “validated” by thetransaction handler, the transaction is placed in the transactionhandler's memory pool (or “mem pool”). A raw transaction that is notfound by the transaction handler to be valid is rejected and not placedin the handler's mem pool.

To this end, upon receipt (i.e. ingress of a raw transaction to thenode), the transaction handler 609 typically carries out two basicactions. As depicted in FIG. 6A, the transaction handler 609 queriesUTXO handlers 614 (at 615) to determine whether inputs to thetransaction exist and, if so, to obtain those inputs (at 616) from theUTXO space being managed by the UTXO handlers 614. If the inputs do notexist, the UTXO handler that receives the query informs the transactionhandler, which then rejects the raw transaction. Upon receipt of inputsfrom the UTXO handler 614, the transaction handler 609 consults asignature verifier 617 (at 618) to determine whether a unlocking script(digital signature) associated with each input is valid. Typically, eachinput contains an unlocking script (digital signature) of thetransaction, and thus the signature verification performed by asignature verifier involves the signature verifier checking that thesignature matches the locking script (pubic key) associated with eachUTXO consumed by the transaction. Further details regarding thisoperation are described below. This check thus involves a cryptographicoperation and is computationally-intensive; thus, the signature verifierpreferably is only consulted by the transaction hander for a valid inputreceived from the UTXO handler. The signature verifier 617 acknowledgesthe validity of the input (in particular, the input signature) at 619.The transaction handler can interact with the UTXO handler and thesignature verifier concurrently as inputs are received by thetransaction handler. Once all input signatures are verified by thesignature verifier 617, the raw transaction is considered by thetransaction handler to the “valid” or “validated,” and at 615transaction handler 609 creates new transactions outputs (UTXOs) in theUTXO handler 614 responsible for UTXOs associated with the newtransaction. In this operation, a create request is sent to only oneUTXO handler, namely the one handler that handles UTXOs in the portionof the transaction id space associated with the transaction. As alsodepicted, the create call (at 615) is sent (after a query and signatureverifier success) to initiate the new transactions outputs (UTXOs).

Once all inputs are verified in this manner, the raw transaction is thenplaced in the transaction handler's mem pool. The raw transaction (thathas now been validated) is then output (i.e. propagated) to all othernodes via 613, and each other node that receives the raw transactioncarries out a similar set of operations as has been just described. Thiscompletes the local validate operation for the raw transaction, which asa consequence is now in the transaction handler's mem pool. Theabove-described process continues as raw transactions are received atthe node (once again, either from edge machines or from other nodes).

Thus, a transaction handler that receives a raw transaction determines(from querying the UTXO handler) whether inputs to the transactionexists and, if so, what are their values and locking scripts (containingpublic keys sometimes referred to as addresses or wallet addresses). Itchecks each input's unlocking script (digital signature), and if allsignatures are valid, the transaction handler commits (saves) the rawtransaction to its associated memory pool. In this manner, validated rawtransactions accumulate in each handler's mem pool. Thus, in eachtransaction handler's mem pool there are a collection of transactions ineffect “waiting” to be mined (i.e., assigned) to a block segment (andthus a block) in the blockchain. Preferably, the system enforces aminimum wait time to allow the new transactions to propagate and bevalidated by the other nodes of the system.

Assume now that the node coordinator 601 determines it is time to mine ablock into the blockchain. The notion of mining a block is distinct fromthe notion of actually adding the block to the blockchain, which happens(as will be described in more detail below) when the node coordinatordecides a block is final according to a prescribed consensus algorithmof the system. Typically, at any given time there is a subset of thenodes that act as “miners.” According to the techniques herein, and ashas been described, in lieu of mining a block as a composite, a block ismined in “segments,” i.e., individual segments of the block are minedseparately (albeit concurrently or in parallel) and, in particular, bythe segment handlers 604.

To this end, and with reference now to FIG. 6B, the node coordinator 601instructs its associated segment handlers 604 to begin mining theirsegments via 605. This command typically includes a start time, aduration, and an end time. The node coordinator also informs other nodecoordinators in the system (via 602) to expect mined block segment datato be transmitted directly (via 607) from the mining node's segmenthandlers to the segment handlers in the other nodes of the system. Asegment handler's job is to obtain and receive validated rawtransactions from a transaction handler's mem pool, and to stage thosevalidated transactions for eventual persistence in the block segment(and thus the block) if and when the block is finalized and added to theblockchain. In an alternative embodiment, the segment handler may obtainand receive digests (hashes) of validated transactions, in which casethe job of staging transactions for future persistence shifts to thetransaction handler.

As will be described, preferably the actual persistence of each segmentin the block (and the persistence of the block in the blockchain itself)does not occur until the segment handlers are instructed by the nodecoordinator to finalize a block. Typically, there is a 1:1 relationshipbetween a segment handler 604 and a transaction handler 609, althoughthis is not a limitation. As noted above, these functions may becombined in an implementation and while a 1:1 relationship is depicted,a node could be configured with any number of either type of handler.

Upon receipt of the command to initiate mining, at 610 the segmenthandler 604 requests the transaction handlers (handling segments for thesegment handler) to assign transactions in their respective mem pools tothe block and return each raw transaction (or a hash thereof). Beforethe transaction handler returns a raw transaction from its mem pool tothe requesting segment handler, however, the transaction handler mustfirst “spend” the transaction inputs with respect to the block beingmined (i.e., apply the actual transaction values to the inputs), whichit does by sending spend requests (via 620) to the UTXO handlers; asdepicted, the UTXO handlers apply the spend requests, update their localdata, and return the result (success or failure) to the transactionhandler (via 621).

In the event of a failure response, the transaction handler mustinstruct the UTXO handlers via 620 to undo all successful spendoperations for the transaction. This collision detection and rollbackconstitutes an optimistic concurrency control mechanism that obviates,and thus avoids the high costs of, acquiring a lock (or a distributedlock in the case of a node with multiple UTXO handlers) on the UTXOhandler(s). This enables efficient high throughput, low latency handlingof UTXO spend operations.

Upon successfully spending all the transaction inputs, the transactionhandler instructs a UTXO handler via 620 to assign the transactionoutputs (the transaction's UTXOs) to the block, and it forwards via 611the raw transaction (and/or a digest thereof) back to the requestingsegment handler.

The segment handler-transaction handler interactions here as justdescribed are carried on as the transaction handler(s) continue toreceive and process the raw transactions as depicted in FIG. 6A anddescribed above. Referring back to FIG. 6B, the segment handlers 604operate in parallel with respect to each other, with each segmenthandler making similar requests to its associated transaction handler.Thus, typically, there is a segment handler-transaction handler pairassociated with a particular segment of the block being mined. Thetransaction handler 609 responds by providing the requesting segmenthandler 604 with each raw transaction from its mem pool, together with adigest that has been computed for the raw transaction. The segmenthandler 604 receives each transaction (and its digest) and sequences thetransactions into a logical sequence for the segment. Each segmenthandler operates similarly for the raw transactions that it receivesfrom its associated transaction handler, and thus the segments for theblock are mined concurrently (by the segment handlers). As the segmenthandler sequences the raw transactions, it takes the digests of thetransactions and outputs them (preferably just the digests) to all ofthe other nodes (via 607). The other nodes of the network use thedigests propagated from the segment handler(s) to validate the segmentthat is being mined locally. A segment handler also receives digestsfrom other segment handlers (in other nodes) via 608.

Once a segment handler 604 determines that a segment is valid, itreturns the result of its processing, namely, the root of a Merkle treecomputed for the segment, to the node coordinator via 606. During miningthe node coordinator trusts that the segments are valid. The othersegment handlers 604 (operating concurrently) function similarly andreturn their mining results indicating that their segments likewisecomplete.

Once all of the segment handlers respond to the node coordinator (withthe Merkle roots of all segments), the node coordinator then computes anoverall block Merkle tree (from all the segment Merkle roots) andgenerates a block header incorporating the overall block Merkle root andother information. The node coordinator then transmits/propagates aMining Done message via 602 containing the block header to the othernode coordinators in the network, and those other node coordinators thenuse the block Merkle root to complete their block verification processas will be described next.

In particular, assume now that the node coordinator 601 receives aMining Start message via 603 transmitted from the node coordinator ofanother node initiating its own block mining operation. This begins ablock verification process for block data mined and transmitted from theother node. The block verification process is a variation on the blockmining process, but the two are distinct and frequently a node will beengaged in both processes simultaneously. Indeed, while a node typicallymines only one block at a time, it can be verifying multiple incomingblocks simultaneously. As with mining, according to the techniquesherein, and as has been described, in lieu of verifying a block as acomposite, preferably a block is verified in “segments,” i.e.,individual segments of the block are verified separately (albeitconcurrently or in parallel) and, in particular, by the segment handlers604.

To this end, via 605 the node coordinator 601 instructs its associatedsegment handlers 604 to receive transaction hashes at 608 from othernodes and, in response, to verify the associated transaction blockassignments made by the mining node's segment handlers as theymine/assign transactions to a block in the mining process. Preferably,verification of segment data is performed progressively (as the data isreceived) and concurrently with the mining/assignment of additionaltransactions to the block segments in the mining node.

Upon receipt of a transaction hash, via 608, a segment handler 604forwards the transaction hash via 610 to the transaction handler 609responsible for handling transactions for the segment. Upon receiving atransaction hash from a segment handler, the transaction handler 609looks up the associated transaction record in its mem pool.

In the event the transaction is missing from the mem pool, transactionhandler 609 sends a request (via 622) to receive the missing rawtransaction (via 623), preferably from the transaction handler in themining node responsible for having mined the transaction. Thisrequest/response action preferably is handled at high priority in anexpedited manner Upon receiving the missing raw transaction, and priorto resuming verification of the transaction's block assignment, thetransaction handler 609 must validate the transaction as described abovebefore adding it to its mem pool.

Upon successfully retrieving the transaction from its mem pool, thetransaction handler performs an assignment of the transaction to theblock segment being verified just as it assigns transactions to blocksbeing locally mined as described above; if, however, the assignmentfails, verification of the segment and the block of which it is a partfails (i.e., the block is rejected).

Subsequently, the node coordinator, applying a prescribed consensusalgorithm, decides to finalize a block. To this end, the nodecoordinator persists the block header, and it instructs the node'ssegment handlers to finalize the block. In so doing, the nodecoordinator provides the overall block Merkle tree to each segmenthandler. Each segment handler, in turn, persists its set of segmentsassociated with the block, and it instructs its associated transactionhandlers to finalize the block. In so doing, the segment handlersgenerate and provide to the transaction handlers the portion of theblock's overall Merkle tree each transaction handler needs for its setof segments. Each transaction handler, in turn, removes the finalizedtransactions from its active mem pool, and it responds to anyoutstanding transaction requests it received from the edge (or wallet)for finalized transactions and, in particular, with a Merkle proofderived from the portion of the block's overall Merkle tree thetransaction handler received from the segment handlers. The transactionhandler then saves the finalized transaction in memory, where it may beused to support subsequent queries that the transaction handler mayreceive concerning the disposition of a transaction. The transactionhandlers then instruct all UTXO handlers to finalize the block. Inresponse, the UTXO handlers mark UTXOs spent in the finalized block aspermanently spent, and mark UTXOs assigned to the finalized block aspermanently created. Persisting the block header and segments to disk inthis manner thus adds the block to the blockchain. Depending onimplementation, the block so written to the blockchain may then beconsidered final (and thus in effect immutable).

Summarizing, in the node processing described above, transactionhandlers receive raw transactions, typically from the edge machines.After a transaction handler validates the raw transaction (and places itin its local mem pool), the transaction handler propagates the rawtransaction to the appropriate transaction handlers in other nodes thatare also responsible for validating that raw transaction. Subsequently,and in response to a determination by the node coordinator to beginmining a block segment, the transaction handler mines (assigns) a set ofraw transactions from its mem pool to the block segment, and sends thoseraw transactions (and their associated digests) to the requestingsegment handler that is handling the respective segment. The segmenthandler sequences the received transactions into the segment and, as itdoes so, the segment handler forwards the list of digests for thetransactions comprising the segment to the other segment handlersresponsible for handling those segments in the other miner nodes. Thus,raw transactions propagate across the transaction handlers in all nodes,but segment handlers preferably only send the transaction digests forthe segments to be verified. During block segment mining andverification, transaction handers consult their local segmenthandler(s), which as noted communicate with the segment handlers ofother nodes. Transaction handlers in different nodes thus communicatewith one another to populate their respective mem pools withtransactions that have been validated (using the UTXO andsignature-verifiers). The segment handlers (and thus the nodecoordinator handling the mining) communicate with one another topopulate the blockchain with a block comprising the segments. Aspreviously noted, the transaction handlers and segment handlers need notbe separate services.

As described above, block verification is similar to block mining,except that for verification the segment handler is feeding transactionhashes to its transactions handlers, which transaction handlers thenrespond with “valid” (with respect to the raw transaction) or “invalid”(with respect to the entire received block), and the latter responseshould not happen unless the miner is behaving erroneously or in anadversarial manner. The above-described technique of generating andhandling of Merkle trees and roots is the preferred cryptographicmechanism that ties transactions to their block. In verification, andupon completion when the node coordinator gets results from all thesegment handlers, the coordinator once again computes the overall blockMerkle root, but this time it compares that root with the root providedin the block header sent to it by the mining block coordinator. If theydo not match, the block is discarded as invalid.

The terminology used herein is not intended to be limiting. As usedherein, the term “validate” is used for the operation that thetransaction handler does when it receives a raw transaction to be put inits mem pool. As noted above, to validate a transaction, the transactionhandler queries the UTXO handler(s) to check the availability of thereferenced UTXOs and talks to the signature-verifier to check signatures(on the inputs). In contrast, the term “verify” is used for the act ofverifying the contents of block segments received from other nodes thatare likewise performing the consensus initiated by the node coordinator.A transaction validation may also be deemed an “initial transactionverification” as contrasted with the “block segment verification” (whatthe coordinator and segment handlers do with block segment data receivedfrom other nodes) in response to the coordinator initiating a miningoperation on the block (comprising the block segments). Also, the term“mine” is sometimes referred to as “assign,” meaning what a transactionhandler does when it is told by the segment handler to assign orassociate a transaction with a block segment, i.e., the transactionhandler's verification of the transaction with respect to its inclusionin a block segment by the segment handler. As noted above, to accomplishthis, the transaction handler communicates with its UTXO handler to“spend” existing UTXOs, and to “assign” new UTXOs to a block segment.

Also, the notion of a “handler” is not intended to be limited. A handleris sometimes referred to herein as a “coordinator,” and the basicoperations or functions of a handler may be implemented as a process, aprogram, an instance, an execution thread, a set of programinstructions, or otherwise.

While the above describes a preferred operation, there is no requirementthat a handler handle its tasks on a singular basis. Thus, a segmenthandler can handle some or all of the segments comprising a block. Atransaction handler can handle the transactions belonging to aparticular, or to more than one (or even all) segments. A UTXO handlermay handle some or all partitions in the UTXO space. The term“partition” here is used for convenience to distinguish from a segment,but neither term should be deemed limiting.

The following provides additional details regarding the above-describednode components in a preferred implementation.

Node Coordination

Node coordinator 601 participates in a network consensus algorithm todecide whether the node should mine a block or not, and from what othernodes it should expect to receive mined block data. If the node is tomine a block, node coordinator 601 sends messages (via 602) to the othernode coordinators in the network. Node coordinator 601 also receivesmessages (via 603) from other node coordinators in nodes that are mininga block. As has been described, node coordinator 601 informs the node'ssegment handler 604 in messages (via 605) to start mining block segmentsand from what other nodes to receive and validate mined block segments.The node's segment handler 604 will return to the node coordinator 601in a message (via 606) the Merkle root of the transactions comprisingeach block segment.

Another aspect of node coordination is managing node localrepresentations corresponding to the one or more chain branches that maybe active in the network at any given time. Typically, a blockchainconsists of a single sequence of blocks up to the point of finalization.Finalization often is set to be some number of blocks deep in the chain,but the decision of what and when to finalize is subject to the rulesgoverning consensus across the network. The part of the blockchain thatis pre-finalized consists of potentially multiple branch chains that getresolved before finalization. As indicated above, for example, whenmultiple nodes mine simultaneously, they fork the blockchain intomultiple branches that have some common ancestor block. The nodecoordinator 601 is responsible for tracking active branches andinforming the segment handlers 604 which branch they are mining, if thenode is mining, and which branch each remote miner is mining.

Segment Handling

As also described, segment handlers 604 handle the generation and/orvalidation of some number of block segments representing a portion ofblock segmentation space. Specifically, the segment handlers begingenerating block segments as directed by the node coordinator 601 inmessages (via 605). When mining, a segment handler 604 transmits minedblock segment data via 607 to segment handlers in the other nodes to beverified. A segment handler 604 receives block segment data in messages(via 608) from segment handlers in mining nodes. To perform transactionmining and validation, a segment handler 604 interacts with anassociated set of transaction handlers 609 as also previously described.

Transaction Handling

Transaction handlers 609 handle the validation of transactions to beadded to the mem pool and propagated to the network, the generation oftransactions to be included in a mined block, and the verification oftransactions to be included as part of a block received from a miningnode. As noted above, the distribution of the transaction segmentationspace may be the same for a transaction handler 609 and a segmenthandler 604, or it may be different. For example, the computationalresources needed by the segment handler function may be sufficiently lowthat only a few such handlers are used to handle all the block segments,whereas the computational resources required by the transaction handlerfunction might be sufficiently high so as to require that each suchhandler manage the transactions for a smaller number of segments thantheir associated segment handler 604.

The transaction handler function plays another important role in thesystem as also previously described, namely, transaction admissions(also referred to as “validation”) and propagation. A transactionhandler 609 receives transactions in messages (via 612) from the edgeeither directly or indirectly via other transaction handlers in thenetwork. The transaction handler 609 validates all received transactionsand if valid, saves the transactions to a pool of unprocessedtransactions (its mem pool) and optionally propagates the transactionsto other nodes in the network in messages (via 613). In this way, thetransaction handler function orchestrates the propagation of transactiondata such that all nodes receive all incoming transactions andassociated incoming transaction digests in a timely and efficientmanner.

UTXO Handling

Preferably, UTXOs are identified by an identifier (txid), which is ahash or digest of the originating transaction, and the index of theoutput in the originating transaction. A UTXO also has two other piecesof information (not used in its identification), namely, a value, and a“locking script.” Generally, the locking script is a set of instructionsor simply a public key associated with the output. Sometimes the publickey is called an address or wallet address. The locking script (e.g.,the public key) is conveyed in the output of a transaction along withthe value, and typically it is stored in a UTXO database along with theUTXO identifying information and its value. Thus, a query to the UTXOhandler during initial transaction validation returns both the value andthe locking script (public key). To spend a UTXO as an input to a newtransaction, the new transaction (essentially its outputs), must besigned by the private key cryptographically matching the public key ofthe UTXO to be spent. This signature is provided with each transactioninput and is generally called the “unlocking script.” The unlockingscript can be a set of instructions or simply a digital signature. Thus,the digital signatures bind the output values of the transaction to thelocking scripts (public keys) for which the receivers of the valuespresumably have the corresponding private key (later used to formulatean unlocking script). The signature verifier does not have the privatekey (as only the wallet or cryptographic element thereof has the privatekey). The signature verifier receives the public key (from the lockingscript) and a signature (from the unlocking script), and the signatureverifier verifies the signature against the public key, thereby provingthe signature was produced by the matching private key. To summarize, atransaction output at a given index has a locking script (public key)and value. A transaction input has the originating txid, index, and anunlocking script (signature).

To handle transactions, and as noted above, the transaction handlerinteracts with a set of UTXO handlers 614 with messages (via 615 and620) to create, query, spend, and assign Unspent Transaction Outputs(UTXOs) associated with each transaction. Each UTXO operation may alsobe reversed using an undo request in messages (via 620). Thisreversibility is valuable because it allows for a transaction handler609 to undo the parts of transactions that may have completedsuccessfully when the transaction as a whole fails to complete. Insteadof locking UTXO databases to allow concurrency and prevent conflicts,here the system preferably relies on detecting conflicts and reversingUTXO operations for partially complete transactions. Conflicts in thiscontext include, but are not limited to, an attempt to spend a UTXObefore it exists or is finalized (as policy may dictate), spending aUTXO that has already been spent by another transaction, or any otherUTXO operation failure that renders the transaction incomplete.

As noted above, each UTXO has a value and an locking script that must beexecuted successfully for the transaction to validate. The script is aset of instructions that must be executed to lock the use of a UTXO asan input to another transaction. Commonly, the script contains publickey material that corresponds to the private key that must be used tosign transactions that consume the UTXO as an input.

Because the number of UTXOs that accumulate can grow large, the UTXOspace preferably is also partitioned by transaction identifier in amanner similar to how blocks are segmented by transaction identifier,although preferably the partitioning and segmentation spaces are dividedaccording the needs of each independently. While UTXO handling could beperformed by the transaction handlers that produce the UTXOs, preferablythe handling of UTXOs is separated out from transaction handling for tworeasons: (1) because the resource demands are different, and (2) becauseisolating the transaction handler function enables the transaction andUTXO handlers to perform more efficiently. Preferably, the UTXO spacealso is partitioned to make more efficient use of a node's aggregatememory and storage resources. By applying this segmentation (namely,through the transaction segmentation space), a highly scalable andtiming-constrained solution is provided.

Signature Verification

The final element in the block diagram in FIG. 6A is the signatureverifier function provided by a set of signature verifiers 617. As notedabove, preferably transactions are signed by the set of private keysassociated with the transaction's inputs. The most compute intensivetask in a node is verifying the signatures of a transaction.Consequently, significant computational resources preferably arededicated to signature verification. Each signature verifier 617preferably harnesses the computational resources necessary to support aportion of the signature verification load, and the transaction handlerfunction disperses the signature verification load across the availableset of signature verifiers 617 using messages (via 618) to send the datato be validated, and in return receiving acknowledgement or negativeacknowledgement in messages (via 619). In one embodiment, theseoperations are carried out by combining signature verification with someother processing (e.g., transaction handling). In another embodiment,and as depicted and described, to allow for greater scalability, theprocessing demand is accommodated by enabling signature verifiers 617separate from other elements.

Pipelined Block Generation, Transmission, and Verification

Referring to FIG. 7 , traditional blockchain based systems serialize thegeneration (mining), transmission, and verification of blocks. In suchsystems, a block is generated 701 by a miner; once the block is finishedbeing generated, it is transmitted 702 to other nodes for verification,and once nodes finish receiving a block, they begin to verify 703 theblock. Such serial-based processing is inefficient and does not scale,especially in the operating context previously described, namely,wherein transaction messages are being generated across a potentiallyglobal-based network.

When attempting to build a system with high performance requirements,e.g., such as being capable of processing millions of real-timetransactions per second, such current implementation approaches areentirely inadequate. For this reason, in the approach herein (and asdescribed above), preferably these processing stages are pipelined forconcurrency. Thus, according to the techniques herein, while a minergenerates 704 block data, previously-generated block data is transmitted705 to nodes for verification. The verifying nodes receive the minedblock data and begin verifying 706 the block's transactions beforereceiving the complete block and likely long before the miner hasfinished mining the block.

It should be appreciated that in accordance with FIG. 5 , the pipelineof block generation, transmission and verification also is instantiatedfor each segment of a block and that, as such, block segments areoperated on in parallel. The result is greater concurrency through thecombination of parallel and pipeline processing.

Streaming Block Generation, Transmission, and Validation

Referring to FIG. 8 , to support pipelined block generation,transmission and verification a streamed block segment generation,transmission and verification process is shown between two nodes,namely: miner node 801 and verifying node 805. Although one verifyingnode 805 is shown, as described above typically all nodes in the networkverify the mined block. As has also been described, this process alsotypically runs concurrently with the same process for other blocksegments being mined by miner node 801. As noted, there may be multipleminer nodes 801 and multiple streamed generation, transmission andvalidation processes operating in the network concurrently. Note that inthis example, the responsibility of staging a segment for persistence isassociated with the transaction handlers as opposed to the segmenthandlers, as described previously.

Generation

As shown in FIG. 8 , the process starts when mining node coordinator 802meets the criteria for mining a block on the network. In one embodiment,this criterion could be a probability condition that the miner can proveit meets (e.g., a trusted or otherwise verifiable random number belowsome threshold). Any criteria for miner selection (leader election) maybe applied. Node coordinator 802 sends messages 809 to request thatmining node segment handler 803 start generating block segments. Nodecoordinator 802 also sends messages 810 indicating to the validatingnode's coordinator 806 to expect mined block segments from the minernode's segment handler 803. Each mining segment handler 803 sendsmessage 811 to their associated transaction handler(s) 804 indicatingthat transaction handler(s) 804 start assigning transactions from a poolof collected raw transactions associated with each transaction handler804 to a block. Transaction handler 804 repeatedly inspects unprocessedtransactions (transactions that have not previously been assigned to theblock or any ancestor thereof) that it received from the edge (directlyor via transaction handlers in other nodes). It should be appreciatedthat some aspects of transaction verification (transaction validation asdescribed above) may be done in advance when the transaction is firstreceived. For each verified transaction assignment, transaction handler804 (1) adds the full transaction record 813 to block segment 831, and(2) sends message 814 containing a digest (e.g., a hash) in a stream tosegment handler(s) 803.

Transmission

Segment handler 803 collects one or more transaction digests from thestream of messages 814 and sends the transaction digests in a stream ofmessages 815 to the segment handler 807 in each validating node 805responsible for validating the generated segment data. As shown, thenumber of messages in the stream of messages 814 may differ from thenumber of messages in the stream of messages 815, though the totalnumber of transaction digests transmitted in both streams typically willbe the same.

In validating node 805, segment handler 807 receives a stream ofmessages 815, extracts the transaction digests, and sends one or moremessages 816 to transaction handler 808. The number of messagescomprising the streams of messages 815 and 816 may differ. In thisembodiment, transmitted message 810, stream of messages 815 ending withmessage 833, and message 823, may be transmitted unicast or multicast,directly from node element to node element, indirectly propagatedthrough elements in other nodes, or routed or forwarded through networkelements. The data may travel aggregated or separated.

Verification

Verifying transaction handler 808 receives the transaction digests andlookups unprocessed transactions it has received from the edge (directlyof via transaction coordinator in other nodes). If the lookup issuccessful, it verifies the transaction assignment. Upon successfulverification, transaction handler 808 (1) sends verificationacknowledgements in messages 818 to segment handler 807, and (2) addsthe full transaction record 817 to block segment 832.

End of Stream Handling

In one embodiment, the streaming generation, transmission, andverification process ends when mining node coordinator 802 sends a stopgeneration message 819 to all mining segment handlers 803. In thisscenario, nodes are assumed to be running asynchronously, and with noexplicit time boundary between execution rounds. In another embodiment,nodes may run in a synchronous manner, and the process would end when aspecific time is reached.

When the process ends, each segment handler 803 sends a stop generationmessage 820 to its associated transaction handler 804. Each transactionhandler 804 finishes or aborts any transaction assignments that arestill in progress and acknowledges that it has stopped mining along withany remaining assigned transactions included in the block segment inmessage 821 to segment handler 803.

Segment handler 803 sends any unsent transaction hashes and anend-of-stream indication in message 833 to validating node's segmenthandler 807. Each segment handler 803 computes a Merkle tree from thetransaction hashes of each segment and sends the Merkle tree root(Merkle root or MR) to the node coordinator 802 in message 822. When thenode coordinator 802 receives a Merkle root for all segments of theblock, it computes the top of the Merkle tree for the overall block fromthe segment Merkle roots and generates a block header composed a hash ofthe previous block header, its mining proof, and the overall blockMerkle root, and other data. On failure, node coordinator 802 send purgemessage 827 to each segment handler 803 which in turn sends a purgemessage 828 to its associated transaction handler(s) 804 that thendiscards the block segment. On success, node coordinator 802 sends theblock header in messages 823 to all validating node coordinators 806.

When each verifying node's segment handlers 807 receives end-of-streamindications in messages 833, they in turn send to their associatedtransaction handlers 808 messages 834 indicating the end-of-streamverification. When each segment handler 807 has receivedacknowledgements for all outstanding transaction assignmentverifications from its associated transaction coordinator 808, itcomputes the Merkle trees for its segments and sends the Merkle root foreach segment in messages 824 to verifying node coordinator 806. Whenverifying node coordinator receives Merkle roots for each segment, itgenerates a block header, and verifies that the block header itgenerates matches the block header it received in message 823. If theblock header does not match, it sends purge message 825 to eachvalidating segment handler 807 which, in turn, sends purge message 826to its associated transaction handler(s) 808 that then discards theblock segment.

Finalizing a Block

As noted above, in the above-described system a block is not persisteduntil it is finalized. Preferably, the block is not finalized until thenode coordinator concludes that is should be finalized based on havingadhered to a prescribed consensus algorithm. In contrast, preferably atthe conclusion of mining, a block is not persisted. Rather, aftermining, a block is simply tracked until it is either finalized (per theconsensus algorithm) or thrown away (purged), in the latter case becauseit did not survive the application of the consensus algorithm.

Thus, and as described, the approach herein leverages a high-quality,low-latency, highly-interconnected core network (the mesh) inconjunction with block segmentation and other above-described features(e.g., topology-aware data propagation, non-blocking architecture,optimistic concurrency control, partitioning, multicast and the otherfeatures) to provide a computationally-efficient transaction processingsystem, all without any central transaction routing or switching (e.g.,a Layer 7 switch that needs to account for an route large numbers oftransactions). Preferably, the architecture is used in conjunction witha global CDN network to provide global reach, and this approachadvantageously enables CDN mapping technologies to be convenientlyleveraged (e.g., by clients and other transaction services) to discoverand interact with the computing elements in the core network.

By way of additional background, leader election and miner selection areactivities performed at prescribed times. In a blockchain system,example scenarios include, but are not limited to, periodic intervals,system initialization, system or component error and failure recovery,and start/stop block generation events.

The distributed system of record described herein provides for apermissioned, highly-secure computing environment comprising a set ofcomputing nodes. For mining, a mining proof is data presented by acomputing node that mathematically proves the node is a legitimate minerof a block or portion thereof. The data preferably is recorded in ablock header such that proper blockchain construction (namely, trust),is self-verifiable. According to this disclosure, mining proof isprovided, preferably using some available source of trusted randomnumbers. In this approach, preferably a node uses a memory-encryptedtrusted computing element to generate real random numbers to facilitateproducing mining proofs that exhibit the properties desired.

The following is an additional glossary of terms used herein.

A blockchain is an append-only immutable chain of data blocks, whereinthe presence of a transaction recorded within a block, and a blockwithin the chain, are verifiable via cryptographic hashes. A block is acollection of transactions. It contains a cryptographic hash linking itto a previous block, forming a chain. Multiple blocks can be linked to aprevious block, but only one finalized block can be linked to a previousblock.

A merchant is an entity that executes a trade of goods or services forpayment. A merchant has a bank account that is managed by an acquiringbank, and typically it maintains point-of-sale terminals (or otherlegacy infrastructure) responsible for generating valid paymentrequests. More generally, a point-of-sale terminal is a type of merchantconnector (MER) that generates payment requests.

A wallet is a collection of private-public key pairs and reference tounspent transaction outputs, which are “stored value,” and that are usedto create transactions. A “wallet service” typically is a softwareentity that securely maintains a collection of wallets, proxies requestsbetween external entities and a core network of computing nodes thatsupport the blockchain, and that process the corresponding responses.

A wallet service may utilize a multiple wallet processor (WP) orequivalent processing function.

As described above, an Unspent Transaction Output (UTXO) is an outputfrom a finalized transaction that contains some value and that isassociated with an address. UTXOs can be passed as an input (spent) to atransaction that is created by a wallet holding the associated privatekey. A UTXO can only be spent once.

An acquirer is an institution where a bank account is held. An acquirertypically operates legacy infrastructure that is responsible forauthorizing payment requests. This infrastructure is sometimes referredto connection module for an acquirer or an operator.

A administrative server is a service external to the payment networkthat provides one or more services, such as clearing, operator andmerchant bank processes, regulatory compliance, and the like.

A ledger service (sometimes referred to as “ledger services”) is adistributed system that processes transactions and maintain a coreledger. The core ledger is the system of record maintained by the ledgerservice utilizing the blockchain technology described herein. The coreledger is a distributed system that processes transactions and createsthe blockchain.

A payment network is a network that combines wallet services and theblockchain core ledger (ledger service). Wallet services receives clienttransactions, routes the transactions to a wallet processor (e.g., aWP), applies the necessary payment logic, and then forwards validtransactions to the ledger services. Ledger services, in turn, receivestransactions from the wallet services, validates, processes, and recordsthem onto the blockchain-based ledger. Processed transactions,consisting of the original legacy transaction and its correspondingblockchain transaction from ledger services, may be stored in a storageservices for long-term persistence. The storage system may be used torespond to historical queries, and to provide backup for disasterrecovery. A payment network may also include a data cooperation serviceto provide an interface to handle administrative traffic. Customertransactions enter the system via wallet services, while administrativerequests (wallet updates, data center updates, historical queries, etc.)enter the system via the data cooperation service, which validatesrequests before forwarding them to the correct service. Preferably, thedata cooperation service exposes a set of RESTful applicationprogramming interface (API) endpoints and, as a result, supports anyclient that can make a TLS mutually-authenticated REST-based HTTPrequest and send data represented by JSON.

UTXO Snapshot Integrity

The above-described design focuses on the major functional units of thesystem and on how to organize and handle the data to meet highperformance requirements. As described, one preferred design involvessegmenting blocks of transactions and partitioning the UnspentTransaction Output (UTXO) data structures. To allow recovery of the highperformance distributed system of record without the necessity to startwith the genesis block, a system that creates a snapshot of the dataperiodically is required. Because the snapshots are necessarily large,and because it takes considerable time to create them, typically it isnot possible to determine a hash of a snapshot at the blocktime that isrepresented by the snapshot. At the same time, and in order to maintainthe correctness properties of the blockchain, it is necessary to recorda hash of the snapshot on the chain. The hash of the snapshot certifiesthe authenticity of the snapshot.

Preferably, snapshots are generated in parallel while the blockchain isbeing generated. Generating the snapshot is time consuming when thenumber of UTXOs is large; e.g., in certain circumstance it may evenrequire hundreds or thousands of block times to create. Once thesnapshot has been created, and according to this disclosure, a hash ofthe snapshot is used to authenticate the snapshot. This hash is thenincorporated into a block header, which is then included in the headerhash that is linked into the rest of the chain.

While the block header stream is generated, the actual transactions mustbe stored for later reference and are required for recovery. Because ofthe time difference between when a snapshot is started and when it iscompleted, the snapshot database typically is stored as it existed atthe specified block depth. Transaction information as well as the blockheader stream, is used to complete the restoration. This layout isdepicted in FIG. 11 . As shown, here the blockchain 1100 comprises theMerkle roots of the transactions contained in the block, e.g., block1102, along with the hash of the previous block. When a snapshot 1104hash is incorporated into a block header, preferably the hash isincluded in the hash used to form the next block. Although the distanceshown between the snapshot and the location of the hash is just sixblocks here in this example, in practice it would more likely be muchgreater, e.g., hundreds or thousands of block times as previously noted.

For snapshot recovery, preferably the following approach is thenimplemented. In particular, to restore the system into a provably-knownstate, the system uses the snapshot (e.g., snapshot 1104), as well asthe chain of transactions that were included in the blockchain while thesnapshot was being recorded. Restoration of the system then comprisesthe following steps: (1) restore the UTXO database (the system state ofall values and addresses in the system), and wherein while restoring thesnapshot, the hash of that snapshot is created; (2) replay each of thetransactions generated starting with the block following the snapshotdepth, and continuing until the block is reached that contains thesnapshot hash is reached; and (3) check the snapshot hash and the blockhash of that block to verify correctly. If everything matches, then therecovery has been successful at the block height indicated by thelocation of the snapshot hash.

Preferably, the above-approach implements snapshot partitioning. Inparticular, and for performance and scalability, preferably both thetransaction streams and the UTXO databases are sharded. This is desiredbecause each group of transactions is independent of other transactions,and because each group of UTXOs is independent as well. When replayingtransactions, each transaction processor and UTXO database (as describedabove) can then be restored independently. Similarly, each snapshot canbe generated independently, and associated transaction logs can bestored independently.

For snapshotting, preferably each UTXO partition is storedindependently. Hashes are then computed for each of the partitions inthe system (which can be larger than the number of UTXO processors).When computing the final checksum for a UTXO snapshot, preferably thehash associated with each partition is combined into a Merkle tree, andthe root of the Merkle tree preferably is then used as the hash for theentire snapshot.

The approach herein has several advantages. It ensures the integrity andself-verifiability of a blockchain/UTXO database snapshot. As has beendescribed, this is accomplished by recording on the blockchain a hash orother digest representation of the snapshot. The technique enables trustand self-verifiability of blockchain snapshots without requiring anexternal trusted actor.

Thus, according to this disclosure, a UTXO database (or portionsthereof) against which the blockchain works is regularly (periodically)snapshotted, e.g., every x minutes. A hash tree over the snapshot isgenerated. The hash is then recorded in a block header, and then aconsensus over it is carried out. The consensus agreement over the UTXOdatabase snapshot facilitate recovery operations, as has been described.

The technique herein may be implemented with UTXO variants. Inparticular, the UTXO concept may be generalized into a more generalconcept of Transaction Output (TXO) exhibiting a variety of behaviorssupporting different use cases. For example, TXOs may be used asReference TXOs. In particular, some business logic systems such asloyalty points and prepaid cards often require some notion of contractor external state. The nature of the contract or external state may wellbe shared across a number of TXOs in the system. Examples would includeexpiration times, “not before” times, and currency (or point) exchangerates, as well as merchant, product, and service restrictions. Moregenerally, the rules and data governing transaction handling in suchsystems can be extremely diverse and complex.

An example is a set of loyalty points, represented by several differentTXOs sharing a common expiration date. If these points are part of aprogram where the expiration date is reset every time there is activityin the account for the point program, there must be a mechanism toefficiently update the expiration dates for each affected TXO. In thiscase, a Reference TXO (RTXO) is employed such that a group of TXOs areassociated with a common RTXO. When the RTXO is updated, all of theassociated parameters with the RTXO are effectively updated or inheritedby the referencing TXOs at the same time.

Another UTXO variant is an Idempotency TXO (ITXO). By way of background,blockchain transactions execute only once and are naturallycollision-resilient. To faciliate using the above-described blockchaintechnology in connection with message regimes that are not native to theblockchain (e.g., legacy ISO8583 based financial systems), support foreither idempotent or collision resilient handling of external messagesis generally required. The database technology required often makes itdifficult and expensive to support these properties in a highly-scalabledistributed manner, and maintaining consistency between the database andthe blockchain is generally not possible in all cases. An IdempotencyTXO (ITXO) is provided to address this scenario. An ITXO enables ablockchain-based ledger to be used as a high performance database forhandling the external messaging. In one embodiment, a blockchain TXOoutput is defined with a key and value and optionally an expiry wherebythe key is derived from, and uniquely identifies, the external message.In this case, the ITXO identity is then the same for all blockchaintransactions that attempt to create it. If multiple blockchaintransactions attempt to create the TXO, at most one will succeed whileothers fail because they attempt to create a TXO that already exists.

Enabling Technologies

As noted above, the techniques of this disclosure may be implementedwithin the context of an overlay network, such as a content deliverynetwork (CDN), although this is not a limitation. In a known system ofthis type, such as shown in FIG. 9 , a distributed computer system 100is configured as a content delivery network (CDN) and is assumed to havea set of machines 102 a-n distributed around the Internet. Typically,most of the machines are servers located near the edge of the Internet,i.e., at or adjacent end user access networks. A network operationscommand center (NOCC) 104 manages operations of the various machines inthe system. Third party sites, such as web site 106, offload delivery ofcontent (e.g., HTML, embedded page objects, streaming media, softwaredownloads, and the like) to the distributed computer system 100 and, inparticular, to “edge” servers. Typically, content providers offloadtheir content delivery by aliasing (e.g., by a DNS CNAME) given contentprovider domains or sub-domains to domains that are managed by theservice provider's authoritative domain name service. End users thatdesire the content are directed to the distributed computer system toobtain that content more reliably and efficiently. Although not shown indetail, the distributed computer system may also include otherinfrastructure, such as a distributed data collection system 108 thatcollects usage and other data from the edge servers, aggregates thatdata across a region or set of regions, and passes that data to otherback-end systems 110, 112, 114 and 116 to facilitate monitoring,logging, alerts, billing, management and other operational andadministrative functions. Distributed network agents 118 monitor thenetwork as well as the server loads and provide network, traffic andload data to a DNS query handling mechanism 115, which is authoritativefor content domains being managed by the CDN. A distributed datatransport mechanism 120 may be used to distribute control information(e.g., metadata to manage content, to facilitate load balancing, and thelike) to the edge servers.

As illustrated in FIG. 10 , a given machine 200 comprises commodityhardware (e.g., an Intel Pentium processor) 202 running an operatingsystem kernel (such as Linux or variant) 204 that supports one or moreapplications 206 a-n. To facilitate content delivery services, forexample, given machines typically run a set of applications, such as anHTTP proxy 207 (sometimes referred to as a “global host” process), aname server 208, a local monitoring process 210, a distributed datacollection process 212, and the like. For streaming media, the machinetypically includes one or more media servers as required by thesupported media formats.

A CDN edge server is configured to provide one or more extended contentdelivery features, preferably on a domain-specific, customer-specificbasis, preferably using configuration files that are distributed to theedge servers using a configuration system. A given configuration filepreferably is XML-based and includes a set of content handling rules anddirectives that facilitate one or more advanced content handlingfeatures. The configuration file may be delivered to the CDN edge servervia the data transport mechanism. U.S. Pat. No. 7,111,057 illustrates auseful infrastructure for delivering and managing edge server contentcontrol information, and this and other edge server control informationcan be provisioned by the CDN service provider itself, or (via anextranet or the like) the content provider customer who operates theorigin server.

The CDN may include a storage subsystem, such as described in U.S. Pat.No. 7,472,178, the disclosure of which is incorporated herein byreference.

The CDN may operate a server cache hierarchy to provide intermediatecaching of customer content; one such cache hierarchy subsystem isdescribed in U.S. Pat. No. 7,376,716, the disclosure of which isincorporated herein by reference.

The CDN may provide secure content delivery among a client browser, edgeserver and customer origin server in the manner described in U.S.Publication No. 20040093419. The approach described there is sometimesreferred to as an SSL-protected edge network. In a typical operatingscenario, secure content delivery enforces SSL-based links between theclient and the edge server process, on the one hand, and between theedge server process and an origin server process, on the other hand.This enables an SSL-protected web page and/or components thereof to bedelivered via the edge server. To enhance security, the service providermay provide additional security associated with the edge servers. Thismay include operating secure edge regions comprising edge serverslocated in locked cages that are monitored by security cameras,providing a key management service, and the like. In one embodimenthere, wallet services may be located in front of or behind anSSL-protected edge network.

In a typical operation, a content provider identifies a content providerdomain or sub-domain that it desires to have served by the CDN. The CDNservice provider associates (e.g., via a canonical name, or CNAME) thecontent provider domain with an edge network (CDN) hostname, and the CDNprovider then provides that edge network hostname to the contentprovider. When a DNS query to the content provider domain or sub-domainis received at the content provider's domain name servers, those serversrespond by returning the edge network hostname. The edge networkhostname points to the CDN, and that edge network hostname is thenresolved through the CDN name service. To that end, the CDN name servicereturns one or more IP addresses. The requesting client browser thenmakes a content request (e.g., via HTTP or HTTPS) to an edge serverassociated with the IP address. The request includes a host header thatincludes the original content provider domain or sub-domain. Uponreceipt of the request with the host header, the edge server checks itsconfiguration file to determine whether the content domain or sub-domainrequested is actually being handled by the CDN. If so, the edge serverapplies its content handling rules and directives for that domain orsub-domain as specified in the configuration. These content handlingrules and directives may be located within an XML-based “metadata”configuration file.

The above-described client-to-edge server mapping technique may be usedto associate a wallet or wallet service (the “client”) with an edgeserver. In a typical use case, a transaction initiated from or otherwiseassociated with that wallet or wallet service then passes through theedge server and onward to the core for further processing as describedherein. As noted above, the wallet or wallet service (or some portionthereof) may also reside inside the edge, such that wallet requests passthrough the edge to the wallet or wallet service and onward to the core.Some portion of the transaction processing may be carried out at theedge server.

Each above-described process preferably is implemented in computersoftware as a set. of program instructions executable in one or moreprocessors, as a special-purpose machine.

Representative machines on which the subject matter herein is providedmay be Intel hardware processor-based computers running a Linux orLinux-variant operating system and one or more applications to carry outthe described functionality. One or more of the processes describedabove are implemented as computer programs, namely, as a set of computerinstructions, for performing the functionality described.

While the above describes a particular order of operations performed bycertain embodiments of the invention, it should be understood that suchorder is exemplary, as alternative embodiments may perform theoperations in a different order, combine certain operations, overlapcertain operations, or the like. References in the specification to agiven embodiment indicate that the embodiment described may include aparticular feature, structure, or characteristic, but every embodimentmay not necessarily include the particular feature, structure, orcharacteristic.

While the disclosed subject matter has been described in the context ofa method or process, the subject matter also relates to apparatus forperforming the operations herein. This apparatus may be a particularmachine that is specially constructed for the required purposes, or itmay comprise a computer otherwise selectively activated or reconfiguredby a computer program stored in the computer. Such a computer programmay be stored in a computer readable storage medium, such as, but is notlimited to, any type of disk including an optical disk, a CD-ROM, and amagnetic-optical disk, a read-only memory (ROM), a random access memory(RAM), a magnetic or optical card, or any type of media suitable forstoring electronic instructions, and each coupled to a computer systembus. A given implementation of the present invention is software writtenin a given programming language that runs in conjunction with aDNS-compliant name server (e.g., BIND) on a standard Intel hardwareplatform running an operating system such as Linux. The functionalitymay be built into the name server code, or it may be executed as anadjunct to that code. A machine implementing the techniques hereincomprises a processor, computer memory holding instructions that areexecuted by the processor to perform the above-described methods.

While given components of the system have been described separately, oneof ordinary skill will appreciate that some of the functions may becombined or shared in given instructions, program sequences, codeportions, and the like.

While given components of the system have been described separately, oneof ordinary skill will appreciate that some of the functions may becombined or shared in given instructions, program sequences, codeportions, and the like. Any application or functionality describedherein may be implemented as native code, by providing hooks intoanother application, by facilitating use of the mechanism as a plug-in,by linking to the mechanism, and the like.

The techniques herein generally provide for the above-describedimprovements to a technology or technical field, as well as the specifictechnological improvements to various fields.

Each above-described process preferably is implemented in computersoftware as a set of program instructions executable in one or moreprocessors, as a special-purpose machine.

The edge network may communicate with the core using varioustechnologies. Representative overlay network technologies that may beleveraged include those described in U.S. Publication Nos. 2015/0188943and 2017/0195161, the disclosures of which are incorporated herein byreference. Among other things, these publications describe the CDNresources being used facilitate wide area network (WAN) accelerationservices over the overlay in general, as well as between enterprise datacenters (which may be privately-managed) and third partysoftware-as-a-service (SaaS) providers. In one typical scenario, aso-called routing overlay leverages existing content delivery network(CDN) infrastructure to provide significant performance enhancements forany application that uses Internet Protocol (IP) as a transport protocolby routing around down links or finding a path with a smallest latency.Another approach is to provide messages from the edge to the core usingmulticast, unicast, broadcast or other packet-forwarding techniques.

The techniques herein generally provide for the above-describedimprovements to a technology or technical field, as well as the specifictechnological improvements to various fields including distributednetworking, distributed transaction processing, wide areanetwork-accessible transaction processing systems, high performance, lowlatency transaction processing systems, non-blocking full meshinterconnect systems, and the like, all as described above.

The nature of the consensus algorithm may vary. Typically, a consensusalgorithm provide Byzantine fault tolerance.

The invention claimed is:
 1. A method operative in association with aset of transaction handling computing elements that comprise a networkcore that receive and process transaction requests into an append-onlyimmutable chain of data blocks, wherein a data block is a collection oftransactions, and wherein presence of a transaction recorded within adata block is verifiable via a cryptographic hash, and wherein UnspentTransaction Output (UTXO) data structures supporting the immutable chainof data blocks are maintained in a UTXO database, wherein a UXTO is anoutput from a finalized transaction that contains a value, comprising:as the append-only immutable chain of data blocks is being generated,periodically snapshotting a given portion of the UTXO database togenerate a snapshot; applying a given function to the snapshot togenerate a hash of the snapshot; recording the hash of the snapshotwithin the immutable chain of data blocks at a location that isdownstream of a block at which the snapshot was initiated, wherein thelocation is determined based on a number of UTXOs in the given portion;and responsive to a receipt of a recovery request, executing a consensusalgorithm over the UXTO snapshot to recover the given portion of theUTXO database.
 2. The method as described in claim 1 wherein the givenportion of the UTXO database is a shard of the UTXO database.
 3. Themethod as described in claim 1 wherein the append-only immutable chainof data blocks is a blockchain.
 4. The method as described in claim 1wherein the hash certifies authenticity of the snapshot.
 5. The methodas described in claim 1 wherein the hash is recorded into a block headerof a block in the append-only immutable chain of data blocks.
 6. Themethod as described in claim 5 wherein the hash is included in a hashused to form a next block of the append-only immutable chain of datablocks at the location.
 7. The method as described in claim 1 whereinthe recovery request is associated with an attempt to restore the set oftransaction handling computing elements into a provably-known state. 8.The method as described in claim 7 wherein a restore into theprovably-known state includes: obtaining the snapshot, together with achain of transactions included in the immutable chain of data blockswhile the snapshot was being created and the hash recorded therein;restoring the UTXO database; while the UTXO database is being restored,re-generating the hash of the snapshot; replaying each of thetransactions generated starting with a first block, and continuing untila given block that contains the snapshot hash is reached; and verifyingthe re-generated snapshot hash and the hash of the given block.
 9. Themethod as described in claim 1 wherein at least one UTXO data structureis configured to include information either in addition to or in lieu ofan address and value to define a Transaction Output (TXO).
 10. Themethod as described in claim 9 wherein the TXO has an associated type.11. The method as described in claim 10 wherein the associated type isone of: a Reference TXO (RTXO), and an idempotency TXO (ITXO).
 12. Amethod operative in association with a set of transaction handlingcomputing elements that comprise a network core that receive and processtransaction requests into an append-only immutable chain of data blocks,wherein a data block is a collection of transactions, and whereinpresence of a transaction recorded within a data block is verifiable viaa cryptographic hash, and wherein Unspent Transaction Output (UTXO) datastructures supporting the immutable chain of data blocks are maintainedin a UTXO database, wherein a UXTO is an output from a finalizedtransaction that contains a value, comprising: sharding the UTXOdatabase into a set of partitions; storing each partition of the UTXOdatabase independently from other partitions in the set of partitions;for at least one partition: periodically snapshotting UTXOs therein togenerate a hash; recording the hash of the snapshot within the immutablechain of data blocks at a location that is downstream of a block atwhich the snapshot was initiated, wherein the location is determinedbased on a number of UTXOs in the partition; and responsive to a receiptof a recovery request, executing a consensus algorithm over the UXTOsnapshot for the at least one partition.
 13. The method as described inclaim 12 wherein the recovery request is associated with an attempt torestore the set of transaction handling computing elements into aprovably-known state.
 14. The method as described in claim 13 wherein arestore into the provably-known state includes: for the at least onepartition: obtaining the snapshot, together with a chain of transactionsincluded in the immutable chain of data blocks while the snapshot wasbeing created and the hash recorded therein; restoring the UTXOdatabase; while the UTXO database is being restored, re-generating thehash of the snapshot; replaying each of the transactions generatedstarting with a first block, and continuing until a given block thatcontains the snapshot hash is reached; and verifying the re-generatedsnapshot hash and the hash of the given block.
 15. The method asdescribed in claim 12 further including snapshotting at least one otherpartition of the set of partitions.
 16. The method as described in claim15 further computing a checksum for a UTXO snapshot that comprises theat least one partition and the at least one other partition.
 17. Themethod as described in claim 15 wherein the at least one partition andthe at least other partition are snapshotted concurrently.